WASHINGTON — Iran has tentatively agreed to ship much of its huge stockpile of uranium to Russia if it reaches a broader nuclear deal with the West, according to officials and diplomats involved in the negotiations, potentially a major breakthrough in talks that have until now been deadlocked.

Under the proposed agreement, the Russians would convert the uranium into specialized fuel rods for the Bushehr nuclear power plant, Iran’s only commercial reactor. Once the uranium is converted into fuel rods, it is extremely difficult to use them to make a nuclear weapon. That could go a long way toward alleviating Western concerns about Iran’s stockpile, though the agreement would not cut off every pathway that Tehran could take to obtain a nuclear weapon.

With a Nov. 24 deadline looming on the nuclear talks, negotiators between Iran and the United States and five other nations are still far from agreement on a range of other issues that could derail a final agreement, including the number of centrifuges the country could keep spinning, the speed at which economic sanctions would be suspended, the fate of a heavy-water reactor that produces plutonium, and whether international inspectors would be free to visit any suspected covert facilities.

But “if the Iran-Russia deal works, it could be the cornerstone of something much larger,” said one American deeply involved in the discussions.

The chief American negotiator, Wendy R. Sherman, alluded to this possible solution to the uranium issue in a recent speech in which she said that “we have made impressive progress on issues that originally seemed intractable.” But Ms. Sherman, who on Monday was named acting deputy secretary of state, has refused to discuss any details of the role Russia could play, saying that negotiations, like mushrooms, “do best in the dark.” As a result, the officials and diplomats would discuss the talks only on the condition of anonymity.

While relations between the United States and Russia have become increasingly difficult in recent months over a range of issues, a senior National Security Council official, while also refusing to discuss details, said on Monday that “it is accurate to say that the Russians have played a very helpful role during these negotiations.”

The official added that Russia had worked with other nations “to put forward creative and reasonable ideas that preserve our objective of cutting off any possible pathway Iran might have to a nuclear weapon.”

“Despite differences of opinion on other foreign policy matters,” the official added, “Russia has remained completely unified with other countries in the negotiations.”

For Russia, the incentives for a deal are both financial and political. It would be paid handsomely for enriching Iran’s uranium, continuing the monopoly it has in providing the Iranians with a commercial reactor, and putting it in a good position to build the new nuclear power reactors that Iran has said it intends to construct in the future. And it also places President Vladimir V. Putin at the center of negotiations that may well determine the future of the Middle East, a position he is eager to occupy.

If the United States is wary of Russia’s role, it has little alternative to involving the country. To expand the time that Tehran would need to build an atomic bomb, it is critical to remove from Iran a substantial amount of the 28,000 pounds of uranium that the International Atomic Energy Agency recently estimated it had produced.

The larger obstacle to reaching an agreement on the uranium may be the Iranians, the senior official said, because “what is less certain is whether Iran will accept the reasonable proposals” on the table, or “will continue to make excessive demands that are not aligned with its practical nuclear needs.”

When Secretary of State John Kerry arrives in Oman this weekend to resume negotiations with his Iranian counterpart, he is expected, among other things, to negotiate over caps that would limit how much uranium Iran could keep on hand at any given time.

But history suggests that an agreement with Iran to part with much of its nuclear stockpile, which it has spent billions of dollars to amass despite Western sanctions and sabotage, is never a sure thing. A deal struck between the Obama administration and Iran in 2009 to ship some of its nuclear fuel out of the country — an agreement that would have left Iran with less than the required amount of uranium to make a single nuclear weapon — fell apart when it was brought to Ayatollah Ali Khamenei, the supreme leader. There is clearly a concern that the same thing could happen again, or that the Revolutionary Guards Corps, which is believed to run the military side of the nuclear program, could object.

And for the Iranians, Russia’s involvement is not necessarily a plus.

“There have been numerous iterations of Iranian-Russian cooperation in the past, and they have not come to fruition,” Karim Sadjadpour of the Carnegie Endowment for International Peace said on Sunday. “Often the economics do not make sense. And the Iranians mistrust the Russians almost as much as they mistrust the United States.”

Russia’s calculus is also complex. It stands to gain financially from the deal, but it also has an incentive to see the nuclear standoff between Iran and the rest of the world continue, because an embargo keeps Iranian oil off the market. With oil prices falling, a flood of exports from Iran could further depress prices.

“This is complicated for Russia,” said Angela Stent, a professor at Georgetown University who specializes in Russian issues. But if Russia salvaged the talks, it would essentially be reprising the role it played in Syria negotiations last year, when it came up with a formula that led President Bashar al-Assad to give up his chemical weapons stockpiles.

For the United States, the fuel agreement would give negotiators more flexibility. If Iran did ship a significant amount of its fuel out of the country, it would allow the United States and its negotiating partners — Britain, France, Germany, China and Russia — to agree to a deal in which the Iranians could be allowed a larger number of centrifuges to spin. A country’s “breakout time,” the time it would take to produce one weapon’s worth of highly enriched uranium, is a function of both how much fuel is on hand and the number and capacity of the centrifuges, the machines that spin at supersonic speeds to purify uranium into reactor fuel — or, at higher concentrations, into bomb fuel.

Mr. Kerry has told Congress that he wants to make sure that Iran’s breakout time is at least a year. Some in Congress, and in the Israeli government, say two years or more is needed to assure that an effort can be detected and stopped. Recently, Iranian officials said the United States had offered to allow Tehran to keep upward of 4,000 centrifuges operating, presumably assuming that there is a reduced inventory of fuel inside the country. But Iran has resisted dismantling any of its 19,000 centrifuges, and the supreme leader has said that ultimately the country plans to operate 10 times that number.

But even if the arrangement is worked out, it is far from clear how a fuel shipment deal would strike critics of the negotiations in Congress.

“Much will depend on the details,” said Robert Einhorn, a Brookings Institution scholar and a former Obama administration official who worked on Iran nuclear issues. If the uranium agreement could be reached, he said, it would give the West “more flexibility to accept a greater number of centrifuges, while still ensuring an adequately long breakout time.” And it would give Iran a face-saving way to “produce fuel for its research reactors and contribute significantly to Russian production of fuel for the Bushehr power reactor,” which Tehran argues is the real purpose of its program, rather than nuclear weapons.

A version of this article appears in print on , Section A, Page 1 of the New York edition with the headline: Role for Russia Gives Iran Talks a Possible Boost. Order Reprints | Today’s Paper | Subscribe